This invention relates to lubricating oils and hydrocarbon fuels containing graft copolymers which impart beneficial properties to these fluids, in particular improvements in dispersancy but also, in the case of lubricating oils, enhanced viscosity and viscosity/temperature relationships. The graft copolymers, when added to the oil, yield lubricants which are excellent dispersants for sludge formed in internal combustion engines, whether spark ignition or compression ignition. The invention further relates to the graft copolymers and methods of preparation.
All lubricants, whatever their service, are exposed to environments which tend to cause the fluid to become dirty with use. The contaminants may be either external in origin, as for example in automotive crankcases where sludge and varnish are formed from a complex reaction of partially burned gasoline and blowby gases, or internal via direct oxidative degradation of the lubricant itself. In either case these deposits, unless dispersed, will settle out of the lubricant causing plugging of filters or even sticking of moving parts where tight tolerances are involved.
A number of additives have been available for many years to attempt to combat this problem. The first used were metal-containing detergents such as alkaline earth sulfonates or phenates. Although these function satisfactorily, they can, once their function is exhausted, contribute to deposits themselves. Furthermore, in certain applications, such as automotive crankcase lubricants, oil that enters the combustion chamber can leave undesirable ash deposits after burning.
Ashless additives, such as polybutene-based succinimides or polyol esters, are superior in this respect and are widely used. They, however, perform only one of the several functions that is demanded of a lubricant. Lubricant additives are called upon not only to provide dispersancy, but also to assure good viscosity-temperature characteristics (to provide adequate flow at low temperatures but still good film thicknesses at high temperature), as well as pour point depressancy, oxidation inhibition, anti-rust and anti-wear properties.
Important performance and economic benefits can be achieved when more than one of these functions can be combined in a single additive. Polymethacrylates have long been known for their excellence in influencing viscosity-temperature characteristics of lubricants. Modifications of the methacrylates can be made to combine dispersancy and viscosity-temperature control in a class of additives commonly known as dispersant viscosity index improvers, of which N-vinylpyrrolidone-alkyl methacrylate copolymers are the prime example. In addition to performing these two functions, such products have the advantage of being ashless.
Recently, a new class of viscosity index improvers, polyolefins, has become available. Probably the best of these, the ethylene-propylene copolymers, have an important advantage over polymethacrylates in that they are far more efficient thickeners, thereby being effective at relatively low use levels. However, the polyolefins are single function additives and their chemical and physical characteristics are such that it has not been possible to incorporate dispersancy without resorting to elaborate, impractical means. In the past, olefinic copolymers have been prepared by (1) direct copolymerization of the monomers, (2) chemical modification of the polymer backbone, or (3) grafting to oxidized, degraded substrates. None of these techniques are needed or used in the present invention. Prior to the use of the special grafting techniques described herein, it has not been possible to prepare dispersant polyolefinic VI improvers without elaborate preparative schemes ("VI" means viscosity index). Accordingly, an object of this invention is to provide a simple and practical method of incorporating dispersancy into these polyolefinic materials, thus combining dispersancy with their unique thickening features.
The additives of the invention are also useful in fuels. In particular, gasoline and middle distillate fuels, such as home heating oils, diesel fuels and jet fuels, tend to deteriorate oxidatively upon standing and form gummy deposits. These deposits can foul screens, burners, or fuel injectors. In the case of gasoline, such gummy residues are deposited in the carburetor, making control of air-fuel ratio impossible. The products of this invention will disperse such deposits, thus preventing deterioration in fuel quality.